Eutrophication is an enormous problem in the Broads. Changes in farming practices and
sewage disposal in the 1950s and 1960s released high levels of
phosphorus and
nitrogen into the Broads, causing eutrophication. Mass decay of plant matter
removes oxygen, damaging fish stocks, preventing recreational fishing. The loss of larger plants and reed fringes in eutrophic waters increases erosion of banks and the buildup of
sediment on lake floors. This impedes navigation and requires costly dredging to remove. The beauty of the area is damaged by eutrophication, which is detrimental to the tourism industry. The Broads Authority and Environment Agency have been working to return the broads to a more natural state since the problem was identified in 1965. The first stage in reversing eutrophication in the Broads is to reduce
phosphate input. Reducing
nitrate input would have a similar effect, but due to the relatively higher
solubility of nitrates, it is harder to control. The discharge of treated sewage was recognised as the main source of phosphates in the waters of the broads. Iron compounds have been used to
precipitate phosphates out of treated sewage in all nine
treatment plants upstream of Barton Broad, initially cutting phosphorus levels in sewage discharge by 90%. High levels of phosphate can remain present in the sediments at the bottom of waterways, preventing dissolved levels decreasing, even when the source is eliminated.
Suction dredging has been used across the Broads to both deepen waterways and remove phosphate-rich
sludge. Without stabilising the compacted
peat beneath the sludge, the peat loosens and can release phosphorus at a similar rate. The growth of larger water plants, which stabilise the floor, is, therefore, necessary to complete the transformation. Even with reduced nutrient levels,
algae tend to remain dominant, blocking light and preventing plants from growing on the floor of the waterway. By manipulating the food chain, a process called
biomanipulation, algae can be removed. To allow
zooplankton to thrive,
planktivorous fish have been largely removed from some Broads, normally by
electrofishing. Around 75% of such fish must be removed for successful treatment. The explosion of zooplankton that results eats almost all algae, creating clear waters. Plants are allowed to naturally recolonise the clearer waterways. The plant growth stabilises the floor, reducing the release of phosphorus. Their own nutrient uptake reduces nutrients available to algae. Larger plants also create a favourable environment for predatory fish such as
pike, which eat planktivorous fish, continuing to control their numbers. These effects tend to create a stable ecosystem where low growing underwater plants dominate. ==Ecology and conservation==